1986 Mercruiser 140 Elec. problem

[brs517]

Can anyone help me with this problem?<br /><br />Battery was dead on the water last weekend. I got a jump start and it ran just fine to get it home, but dead again once I shut it off. Hooked up my volt meter to the battery and it shows about 12.6v when not running and 12.5v when the engine is running. So, it's not charging, right?<br /><br />What I've done so far:<br /><br />Took battery in to be checked-OK<br /><br />Alternator & Voltage Regulator checked OK <br /><br />Belt tension OK<br /><br />Checked my connections, and cleaned the ones that looked even slightly corroded<br /><br />Checked Ohms on the main output wire from the alternator to the positive cable to the battery...read at about 4.5 ohms...that's ok, right?<br /><br />I'm running out of ideas!!! Can anyone help??<br /><br />Thanks,<br />Brian

 

[Bondo]

Re: 1986 Mercruiser 140 Elec. problem

Alternator & Voltage Regulator checked OK

No Way......<br />It's Not Charging......<br />Should be 13.6 volts Running......

 

[Bhamil]

Re: 1986 Mercruiser 140 Elec. problem

Bondo is right, BRS. That alternator is not charging. Bondo states 13.6VDC and I agree, and it can get up to 14.6VDC at higher RPM's. That's not saying the alternator is bad, though, because there are some other things you need to check. Disconnect the battery/ies at the positive terminal/s. Then, from the alternator, trace the large red wire back to the starter motor and ensure it's connections are clean and tight. Trace all wires that are common to that primary wire and make sure they are connected solidly and cleanly. Remember a voltage test on a battery and alternator means very little because it's the ability of either or both to perform under a load and that's an amperage issue. A battery can provide 12VDC (a measure of the "pressure" of volts available) and not take a load in amps (the measure of the volume of free electrons available in the battery). You don't want to get into trying to measure amps personally, but, you can take the alternator to a reputable shop and have it LOAD tested. Most testers will give a dummy load (static test) to 80 amps and that's a solid test (in the boat the load can exceed that but that's dynamic and there's a difference). Have the battery tested out of the boat. You'll discover your problem along the way, I'll bet you a seafood dinner!

 

[rodbolt]

Re: 1986 Mercruiser 140 Elec. problem

hello<br /> carefully test the purple wire for 12v DC when the key is on if it is a 3 wire alt. if it is a self exciting 1 wire check for 12v at the alt post and make sure the orange wire is clean.<br /> good luck and keep posting

 

[DHPMARINE]

Re: 1986 Mercruiser 140 Elec. problem

brs517 Don't overlook the 'other'end of the cables.Check the ground cable where it attaches to the engine (usually the flywheel housing).Also 'pull' on the cables when they are attached.Make sure none are elastic.(Hollow inside... rotted out)<br />DHPMARINE

 

[fireship1]

Re: 1986 Mercruiser 140 Elec. problem

Hello, Dhpmarine has brought up an excellent point. I had a problem similar to this last year on my mercrusier 140. The alternator load tested OK off the boat. All wire termination's were clean and tight. I was stumped! At least until I FELT the large orange supply wire coming off of the alternator. At idle speed it was getting HOT! Hot to the point of burning my finger if I held it there. Turns out the harness was stretched way too tight. The wire was stranded cable, most of the strands had broken free within the insulation. All of that amperage was coursing through about one or two stands of wire! Grabbing that part of the wire where the hot spot was and pulling caused the wire to snap instantly revealing the fault. I replaced that wire from the large cannon plug on the starboard side of the engine compartment all the way back to the alt with a heavy stranded cable. I believe I used about 6 awg stranded. No more trouble after that! Maybe this might be something to look into.

 

[Bhamil]

Re: 1986 Mercruiser 140 Elec. problem

Fireship1; Your experience sounds similar to mine and you found the problem a lot quicker than I did. I'm glad you posted the solution because I ended up replacing almost all the wiring in the charging system before I found the culprit. And I forgot to mention it in my original post! Good job, and good advice.

 

[fireship1]

Re: 1986 Mercruiser 140 Elec. problem

Hello, Thanks Ben! I guess I got lucky with that day of troubleshooting! Other days didn't always go as smooth as that! To this day IM not 100% sure if pure stress of a wire being pulled too tight caused it, or if a small pinhole in the insulation caused a bit of corrosion within the copper stands caused it to break. Or maybe a bit of both! The wire in question was a slight bit corroded where the break was found. Maybe a contributing factor? I think brs517 should look at this wire closely maybe a posable problem. If the wire looks OK from the outside a quick reading on the cable for total ohms with a multimeter will prove the wire good or otherwise. Brs517, hope this info helps you! Good luck!

 

[Bhamil]

Re: 1986 Mercruiser 140 Elec. problem

Fireship1; Your welcome. I guess I would conclude there comes a time in the life of marine electrical stuff you just have to replace the wiring, maybe before it leaves you stranded the first time. I have some background in marine electronics and I know that any unprotected copper wire will corrode very quickly, and salt leaches like crazy, making it worse. So I would advise BRS to begin the process of replacing all the wiring in the engine well, over time, starting with the charging system, if it shows even the slightest evidence of wear. If it's solid, maybe not. But, as you experienced, the wiring at least needs to be inspected on a regular basis.

 

[brs517]

Re: 1986 Mercruiser 140 Elec. problem

Thank you all. Fireship, you were right on, but unfortunately I posted this last Summer and had to find it the hard way, without the benefit of your advice. The orange wire was corroded back from the terminal about an inch, held together with just 2 or 3 strands. Good call!<br /><br />Brian